Cystic fibrosis (CF) airway epithelia have many defects including a loss in chloride (Cl-) and fluid transport, a loss in mucociliary clearance, a loss in apical autocrine and paracrine ATP signaling, and a gain in Na+ transport. Exogenous nucleotide agonists restore extracellular APT signaling and stimulate Cl- and fluid transport in cystic fibrosis (CF) airway epithelia. As such, aerosolized nucleotide agonist therapy has been proposed to treat CF airways. To understand how nucleotide agonists regulate CF and non-CF airway epithelial function, a complete understanding of plasma membrane purinergic receptors is required. Preliminary data from our laboratory reveal that a new class of purinergic receptor, the P2X receptor channels (P2XRs), are expressed by airway epithelia. The cellular and molecular physiology of P2XR expression and function has not been studied in epithelia. P2XRs are ligand-gated channels that bind ATP in an extracellular domain and form intrinsic calcium (Ca2+)- permeable, non-selective cation channels in the plasma membrane. ATP-gated P2XRs may affect epithelial cell function by mediating influx of Ca2+ from extracellular stores or by triggering Ca2+- dependent protein kinase signaling. Therefore, we will test the central hypothesis that: P2X purinergic receptor channels are expressed by airway epithelia and function as ATP-gated Ca2+ influx channels to regulate Cl-, Na+, and fluid transport across airway epithelia. Because little is known about P2XRs in airway epithelia, we anticipate that new and exciting results will be found. Because our preliminary data demonstrate that P2XR expression is similar in CF versus non-CF airway epithelia and beacuase P2XR agonists stimulate Cl- secretion across both CF and non-CF mouse and human airway epithelium in vitro and in vivo, activation of P2XRs may provide a novel approach with which to restore normal Cl-, Na+, and fluid transport across CF airways and improve mucociliary clearance from CF lungs.